1. Field of the Invention
The present invention relates to a lens apparatus and an image pickup apparatus including the lens apparatus, and more particularly, to a lens apparatus including an anti-reflection film having a subwavelength structure for anti-reflection property that is formed on an optical surface of an optical member in the lens apparatus, and to an image pickup apparatus including the lens apparatus.
2. Description of the Related Art
Conventionally, there is a concern about deterioration of image quality due to unnecessary reflection light on an optical element surface, which is called ghost or flare. Therefore, there is proposed an invention of an optical system using an anti-reflection film that can realize a low reflectance in a wide incident angle range.
For instance, Japanese Patent Application Laid-Open No. 2005-316386 discloses a technology of forming an anti-reflection film including at least one layer formed by using a sol-gel method on a light transparent member having a concave surface facing an aperture stop. Japanese Patent Application Laid-Open No. 2009-139775 discloses a technology of forming an anti-reflection structure formed of multiple micro convex/concave structures at an average pitch of 400 nm or smaller in at least one part in an optical system in which a concave lens surface and a convex lens surface are opposed to each other with an air layer therebetween.
In order to obtain a good anti-reflection effect in a wide wavelength range and in a wide incident angle range, it is important to appropriately set where to apply the anti-reflection film on the lens surface constituting the optical system. However, under the conditions of Japanese Patent Application Laid-Open No. 2005-316386 or Japanese Patent Application Laid-Open No. 2009-139775, the application part is set insufficiently so that a sufficient anti-reflection effect cannot be obtained.